Chlorofluorocarbons (CFCs) have been used in refrigerators and air conditioners for many years. Dichlorodifluoromethane or refrigerant 12 (R12) has been the refrigerant of choice for automotive air conditioning systems ever since it was developed in 1930. The history of this development is discussed in detail in "Development of Chlorofluorocarbon Refrigerants", by R. Downing, ASHRAE Transactions 90 pt. 2, pp. 481-91, 1984. R12 is widely used in automobiles because it is non-flammable, low in toxicity, and compatible with the lubricants used in automotive air conditioning systems. Moreover it has the right combination of physical properties, such as boiling point and vapor pressure, to permit efficient use in these systems. However, over the years, large amounts of R12 have been released into the atmosphere as a result of damaged, leaky, or abandoned air conditioners as well as routine maintenance on these devices.
In 1974, it was postulated that chlorofluoromethanes as well as other chlorofluorocarbons are damaging to the earth's ozone layer. This research was reported in "Stratospheric SInk for Chlorofluoromethanes: Chlorine atom catalyzed Destruction of Ozone" by M. J. Molina and F. S. Rowland, Nature, 249:810-12, 1974. This theory has been confirmed recently by the discovery of ozone "holes" over the Arctic and Antarctic. Richard A. Kerr reported in Research News, pp. 1489-92, Mar. 25, 1988, that the ozone layer over latitudes corresponding to the United States has reduced about 5%.
The ozone layer acts as a barrier to UV radiation from the sun. Since UV radiation damages living organisms, destruction of the ozone layer would have a serious impact on life on this planet. In fact there is strong evidence that human skin cancer rates are on the rise and that phytoplankton in the ocean have been reduced by 25%.
This has resulted in a world-wide effort to eliminate release of ozone depleting CFCs into the atmosphere, culminating in Montreal in 1987 in the signing of an international agreement. The "Montreal Protocol" sets up a world-wide process to reduce production and consumption of materials that can damage the ozone layer. In response to this agreement, the aerosol, industrial cleaning and foam insulation industries are starting to use alternatives to CFCs. There was report of a proposal to ban automotive air conditioners in the Los Angeles Times on Jul. 18, 1989.
The ideal replacement refrigerant would be a single compound: failing that an azeotropic or near-azeotropic mixture would work. An azeotrope is a mixture whose composition and physical properties remain constant with evaporation. A near-azeotrope is a mixture whose composition and physical properties remain nearly constant with evaporation. While several investigators have researched replacements for automotive air conditioner refrigerants, the best replacements so far, 1,1,1,2-tetrafluoroethane (R134a) and a blend covered by U.S. Pat. No. 4,810,403, suffer from serious deficiencies. Since R134 a contains no chlorine, is not compatible with the lubricants used in present automotive air conditioners. Although the patented blend is compatible with such lubricants, it is not azeotropic and thus refrigerant leaks could substantially change its pressure characteristics.
If a near-azeotropic refrigerant mixture could be found that was non-flammable, low in toxicity, compatible with the lubricants used in automotive air conditioning systems, had the right combination of physical properties, such as boiling point and vapor pressure, to permit efficient use in these systems, and was less damaging to the Earth's ozone layer it would satisfy a long felt need in the field of automotive air conditioning technology. Use of this refrigerant would eliminate atmospheric damage caused by automotive air conditioners, ensure compliance of automotive air conditioner systems with international agreements and thus eliminate the need to ban such air conditioners.